1. Field of the Invention
The present invention relates to a radiation imaging apparatus, a control method for the radiation imaging apparatus, and a program. Especially, the present invention is suitable for an X-ray imaging apparatus including a C-shaped arm used in an operating room, or the like.
2. Description of the Related Art
The radiation imaging apparatus is a real-time observation apparatus. The radiation imaging apparatus is used, for example, in an operation using catheters, to display the state of the moving catheter in real time in order to determine to which direction the operator is to move his/her hand without injuring the organ.
In recent years, in the field of the radiation imaging apparatuses, in place of X-ray image intensifiers, in order to increase the resolution, reduce the volume, and reduce the distortion of an image, large-area flat-panel type radiation imaging apparatuses of an equal-magnification optical system using a photoelectric conversion device have been widely used.
One of the flat panels of equal-magnification optical system used for the radiation imaging apparatuses, there is a large-area flat panel which is made by two-dimensionally connecting image sensors generated on a silicon semiconductor wafer by a complementary metal-oxide semiconductor (CMOS) semiconductor manufacturing process. For example, Japanese Patent Application Laid-Open No. 2002-026302 discusses a manufacturing method of a large-area flat panel. In the method, in order to implement an imaging area with a size larger than a silicon semiconductor wafer in the large-area flat panel, rectangular image sensors cut in a strip shape from the silicone semiconductor wafer are tiled to form the large-area flat panel.
By simultaneously reading pixel data from a plurality of tiled image sensors, the reading speed of the pixel data of one image can be increased, so that the imaging cycle can be shortened and the real-time performance can be increased. However, the pixel data simultaneously read from the plurality of tiled image sensors cannot be directly displayed as it is, and also the data is not appropriate for image processing. Accordingly, the data needs to be converted into a raster image. The raster image is data for representing an image in a series of dots, and suitable for processing data such as a complicated figure and a photograph.
FIG. 11 illustrates an example of the two-dimensionally tiled image sensors. In the example in FIG. 11, in the large-area flat panel, four sheets in the horizontal direction, two sheets in the vertical direction, a total of eight sheets of image sensors 121 to 128 of the same performance are two-dimensionally tiled. External terminals for drive control and data output of the image sensors 121 to 128 are disposed at one short side of the individual image sensors. The upper frame and the lower frame of the image sensors are tiled such that short sides opposite to the external terminal sides face each other.
In the configuration, in the upper frame including the image sensors 121 to 124, the upper left point, the horizontal direction, and the vertical direction are regarded as the origin, the main scanning direction, and the sub-scanning direction respectively. In the lower frame including the image sensors 125 to 128, the lower right point, the horizontal direction, and the vertical direction are regarded as the origin, the main scanning direction, and the sub-scanning direction respectively. Further, reading the image data of the image sensors 121 to 128 that form the large-area flat panel is performed for pixel by pixel in order starting from the origin to the main scanning direction.
If the same reading clock is used in the eight image sensors 121 to 128, the image data pieces are simultaneously read from the image sensors 121 to 128. As a result, as compared to a case where the data is read from the image sensors one by one, the image data of one frame can be acquired at a speed eight times faster. However, it is not possible to directly display the read data on a monitor. Accordingly, the pixel data pieces read from the image sensors 121 to 128 are written in a frame memory while write addresses are appropriately updated.
FIG. 12 illustrates the order of reading the image data from the frame memory. As illustrated in FIG. 12, starting from the upper left as the origin, to the horizontal direction as the main scanning direction, and then in the vertical direction as the sub-scanning direction, the pixel data is stored in the frame memory. Then, the image data is successively read one pixel at a time from the frame memory, so that the data is converted into a raster image that can be displayed on the monitor.
FIGS. 13A and 13B are timing charts illustrating timing of reading the pixel data from the large-area flat panel and timing of outputting the raster image. FIGS. 13A and 13B include shooting triggers 1301 and 1311, timing 1302 and timing 1312 of a start of reading the pixel data from the large-area flat panel, and timing 1303 and timing 1313 of an end of reading of the pixel data from the large-area flat panel. FIGS. 13A and 13B further include timing 1304 and timing 1314 of a start of reading of the pixel data from the frame memory, timing 1305 and timing 1315 of an end of reading of the pixel data from the frame memory, timing 1306 and timing 1316 of a start of outputting the image data, and timing 1307 and timing 1317 of an end of outputting the image data.
First, output delay is described with reference to FIG. 13A. As illustrated in FIG. 13A, at the timing 1303 of the end of reading of the image data of one frame from a large-area flat panel 107, if reading of the image data from the frame memory starts at the timing 1304, between the start of shooting by the shooting trigger 1301 to the timing 1307 of the end of outputting the image data, output delay time of a little less than two frames occurs.
Next, a passing phenomenon is described with reference to FIG. 13B. As illustrated in FIG. 13B, if the timing 1314 of the start of reading the image data from the frame memory is too early, a phenomenon referred to as a passing phenomenon occurs. In the passing phenomenon, image data that is not yet written in the frame memory is tried to be read occurs.
To solve this issue, Japanese Patent Application Laid-Open No. 2008-117135 discusses a technique for performing appropriate control in reading image data. In the technique, when dividing and reading the image data from a dynamic random access memory (DRAM) while writing the image data in the DRAM, the read processing of the image data is controlled so as not to pass the write processing.
However, when writing or reading the pixel data in/from the frame memory is stopped to avoid the occurrence of the passing, the reading process of the pixel data from the frame memory is interfered every certain cycle, and accordingly, the real-time performance is decreased.
Further, in a case of a system for performing image processing, or the like in response to an end of outputting the image data of one frame, if the access is stopped as described above, the image data output processing may be interfered. Then, the image data output of each frame does not end at the constant cycle. As a result, flicker due to jitter of the frame or the like occurs in the image data on which the image processing is performed. Further, the write address of the pixel data to the frame memory differs in each pixel data read from the image sensor. Accordingly, a memory control unit for monitoring the addresses may be complicated.